1. Field of the Invention
The present invention relates to heat transfer components. More particularly, the present invention relates to heat pipes and to beat pipes employing diamond components therein to improve the properties of heat pipes with respect to their thermal transfer performance and other characteristics.
2. The Prior Art
Heat pipes are well-known devices that effect the transport of heat from a source to a sink with very high efficiency and power handling capacity compared to heat transfer through ordinary solid components. Heat pipes commonly consist of a closed plenum, or space, said space being partially filed with a substance or heat exchange medium (a working fluid) which is a liquid at the temperature of the cooler end (heat sink region) of the heat pipe and which is a gas at the temperature of the warmer end (heat source region) of the heat pipe.
The plenum is often also partially occupied by a fibrous material that serves as a capillary mass that effects transport of liquid heat exchange medium from the heat sink region to the heat source region, at which the liquid heat exchange medium vaporizes, absorbing heat from the heat source, and is then transported by means of its own pressure to the heat sink region, at which it recondenses to a liquid, yielding up its heat of vaporization and effecting transport of heat energy from the heat source to the heat sink. Capillary action then transports the condensed heat exchange medium back to the heat source to renew the cycle. A schematic view of a heat pipe and its operation is presented in FIG. 1.
Because of the relatively large amount of heat that is required to drive the continuous vaporization and condensation cycle, heat pipes can exhibit an effective thermal conductivity of over 100 times that of any known bulk material. By suitable choice of structural materials, heat exchange fluids, and capillary materials, heat pipes have been made to operate at temperatures ranging from cryogenic to 2000 degrees Centigrade. Their excellent thermal transport properties and mechanical simplicity have led to their widespread adoption in thermal management systems that require efficient transport of heat from sources to sinks.
A specific example of heat pipe utility is their employment in laptop and similarly thermally constrained computer systems. Microprocessors and their ancillary integrated circuits generate heat during operation. In general, the faster such devices operate, the more heat they generate. In computers that require high packaging densities to achieve small size, such as laptop personal computers, it is very difficult to provide for adequate heat rejection to maintain safe and reliable operation of microprocessors and other integrated circuits. Heat pipes have made a great contribution to solving this problem.
An increasing portion of laptop computers incorporate heat pipes to transport heat from the processor and other internal heat sources to a large-area heat sink that exchanges heat with surrounding air. As microprocessor heat loads increase, heat pipe technology becomes increasingly the thermal transport technology of choice, indeed the only practical technology, for maintaining processor temperatures within operating limits.
It is appreciated by those skilled in the art that heat energy, in order to be transported by the heat pipe, must first pass from its source, across the wall of the heat pipe, into the heat exchange fluid which then vaporizes to effect further transport of the heat energy. The heat must again pass across the wall of the heat pipe to the heat sink at the condensation (heat removal) end of the heat pipe. The walls of the heat pipe, being composed of materials having much lower thermal conductivity than the effective thermal conductivity of the heat exchange liquid/vapor phase change action, present a resistance to transfer of heat from the source to the working fluid. It is this critical wall thermal resistance towards which this invention is directed.
Thermal transport across the wall of a heat pipe is a direct function of the thermal conductivity of the wall material. This drives toward selection of a high thermal conductivity material, such as copper or silver, for use in the thermal transfer wall. However, the wall material must also be compatible with the contemplated operating temperature range, working fluid, and system components. This often dictates use of materials with inferior conductivity, such as steel, aluminum, or other material less desirable from a heat transfer perspective.
The present invention is a heat pipe employing diamond as the thermal transfer wall material through which heat is transported into and/or out of the heat pipe. Several improvements that are of great utility result from this invention which will be described below following a brief review of the properties of diamond that particularly suit it for this invention.